Image processing device, image processing method, and image processing program

Abstract

An image processing device includes: a detecting section configured to detect, from a frame image, a local-maximum region that is configured of pixels each having a color-difference signal value larger than color-difference signal values of surrounding pixels; a determining section configured to determine an overlapping region where the local-maximum region overlaps with a first neighboring region of a pixel of interest that belongs to the local-maximum region, and to determine a minimum of color-difference signal values of pixels that belong to the overlapping region; and a correcting section configured to correct a color-difference signal of the pixel of interest, based on both a color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region.

What is claimed is: 
     
         1 . An image processing device, comprising:
 a detecting section configured to detect, from a frame image, a local-maximum region that is configured of pixels each having a color-difference signal value larger than color-difference signal values of surrounding pixels;   a determining section configured to determine an overlapping region where the local-maximum region overlaps with a first neighboring region of a pixel of interest that belongs to the local-maximum region, and to determine a minimum of color-difference signal values of pixels that belong to the overlapping region; and   a correcting section configured to correct a color-difference signal of the pixel of interest, based on both a color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region.   
     
     
         2 . The image processing device according to  claim 1 , wherein the correcting section corrects the color-difference signal of the pixel of interest, based on a difference between the color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region. 
     
     
         3 . The image processing device according to  claim 1 , wherein
 the determining section determines, for the pixel of interest, a first minimum value and a second minimum value, the first minimum value being defined as a minimum of color-difference signal values of pixels arranged in a first direction within the overlapping region, and the second minimum value being defined as a minimum of the color-difference signal values of pixels arranged in a second direction within the overlapping region, and   the correcting section corrects the color-difference signal of the pixel of interest, based on both the color-difference signal value of the pixel of interest and the first and second minimum values.   
     
     
         4 . The image processing device according to  claim 3 , wherein the correcting section determines a first correction value based on both the color-difference signal value of the pixel of interest and the first minimum value, determines a second correction value based on both the color-difference signal value of the pixel of interest and the second minimum value, and then corrects the color-difference signal of the pixel of interest based on a larger one of the first correction value and the second correction value. 
     
     
         5 . The image processing device according to  claim 1 , wherein
 the color-difference signal includes a first kind of color-difference signal and a second kind of color-difference signal,   the determining section determines a first minimum value and a second minimum value based on the first kind of color-difference signal, the first minimum value being defined as a minimum of first kind of color-difference signal values of pixels that are arranged in a first direction within the overlapping region, and the second minimum value being defined as a minimum of the first kind of color-difference signal values of pixels that are arranged in a second direction within the overlapping region, and determines a third minimum value and a fourth minimum value based on the second kind of color-difference signal, the third minimum value being defined as a minimum of second kind of color-difference signal values of pixels that are arranged in the first direction within the overlapping region, and the fourth minimum value being defined as a minimum of the second kind of color-difference signal values of pixels that are arranged in the second direction within the overlapping region, and   the correcting section corrects the first kind of color-difference signal of the pixel of interest based on both a first kind of color-difference signal value of the pixel of interest and the first and second minimum values for the first kind of color-difference signal, and corrects the second kind of color-difference signal of the pixel of interest based on both a second kind of color-difference signal value of the pixel of interest and the third and fourth minimum values for the second kind of color-difference signal.   
     
     
         6 . The image processing device according to  claim 4 , further comprising a gain determining section configured to determine a first gain and a second gain for the pixel of interest,
 the gain determining section determining the first gain based on a first signal variation that is a luminance signal variation of the pixels arranged in the first direction, and determining a second gain based on a second signal variation that is a luminance signal variation in the second direction,   wherein the correcting section adjusts the first correction value based on the first gain, and adjusts the second correction value based on the second gain.   
     
     
         7 . The image processing device according to  claim 6 , wherein
 the first signal variation is a difference between a first average value and a second average value, the first average value being defined as an average value of the luminance signals of pixels arranged in a predetermined zone on one side of the pixel of interest in the first direction, and the second average value being defined as an average value of the luminance signals of pixels arranged in a predetermined zone on other side of the pixel of interest in the first direction, and   the second signal variation is a difference between a third average value and a fourth average value, the third average value being defined as an average value of the luminance signals of pixels arranged in a predetermined zone on one side of the pixel of interest in the second direction, and the fourth average value being defined as an average value of the luminance signals of pixels arranged in a predetermined zone on other side of the pixel of interest in the second direction.   
     
     
         8 . The image processing device according to  claim 6 , wherein
 the first gain increases as the first signal variation increases, and   the second gain increases as the second signal variation increases.   
     
     
         9 . The image processing device according to  claim 6 , further comprising a converting section configured to convert a color signal into the color-difference signal and the luminance signal,
 wherein the gain determining section determines, for the pixel of interest, the first gain based on both the first signal variation and a third signal variation that is a color signal variation of the pixels arranged in the first direction, and determines the second gain based on both the second signal variation and a fourth signal variation that is a color signal variation of the pixels arranged in the second direction.   
     
     
         10 . The image processing device according to  claim 3 , wherein
 the first direction is a horizontal direction, and the second direction is a vertical direction.   
     
     
         11 . The image processing device according to  claim 3 , wherein
 the first direction is a direction along a straight line passing through both an upper left pixel located on a upper left side of the pixel of interest and a lower right pixel located on a lower right side of the pixel of interest, and   the second direction is a direction along a straight line passing through both a lower left pixel located on a lower left side of the pixel of interest and an upper right pixel located on a upper right side of the pixel of interest.   
     
     
         12 . The image processing device according to  claim 2 , wherein the correcting section corrects the color-difference signal of the pixel of interest based on color-difference signals and luminance signals of the pixel of interest and its neighboring pixels, as well as based on the difference between the color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region. 
     
     
         13 . The image processing device according to  claim 1 , wherein the determining section selects, one by one, the pixel of interest from all or some of pixels in the frame image. 
     
     
         14 . The image processing device according to  claim 1 , further comprising a scale-down section generating a scale-down frame image based on the frame image, wherein
 the detecting section detects the local-maximum region from the scale-down frame image, and   the correcting section produces a scale-down correction amount map for the scale-down frame image based on both the color-difference signal value of the pixel of interest and the minimum of the color-difference signal values, produces a correction amount map through enlarging the scale-down correction amount map, and then corrects the color-difference signals of pixels in the frame image based on the correction amount map.   
     
     
         15 . The image processing device according to  claim 1 , wherein the detecting section detects the local-maximum region through comparing a color-difference signal of a pixel in the frame image with color-difference signals of a plurality of pixels located outside a second neighboring region of the pixel. 
     
     
         16 . An image processing method, comprising:
 detecting, from a frame image, a local-maximum region that is configured of pixels each having a color-difference signal value larger than color-difference signal values of surrounding pixels;   determining an overlapping region where the local-maximum region overlaps with a first neighboring region of a pixel of interest that belongs to the local-maximum region;   determining a minimum of color-difference signal values of pixels that belong to the overlapping region; and   correcting a color-difference signal of the pixel of interest, based on both a color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region.   
     
     
         17 . A non-transitory tangible medium having a computer-readable program embodied therein, the computer-readable program allowing, when executed by an image processing device, the image processing device to implement an image processing method, the method comprising:
 detecting, from a frame image, a local-maximum region that is configured of pixels each having a color-difference signal value larger than color-difference signal values of surrounding pixels;   determining an overlapping region where the local-maximum region overlaps with a first neighboring region of a pixel of interest that belongs to the local-maximum region;   determining a minimum of color-difference signal values of pixels that belong to the overlapping region; and   correcting a color-difference signal of the pixel of interest, based on both a color-difference signal value of the pixel of interest and the minimum of the color-difference signal values of pixels that belong to the overlapping region.